An antibody is composed of four polypeptides: two heavy chains and two light chains. The antigen binding portion of an antibody is formed by the light chain variable domain (VL) and the heavy chain variable domain (VH). At one extremity of these domains six loops form the antigen binding site and also referred to as the complementarity determining regions (CDR). Three CDRs are located on the VH domain (H1, H2 and H3) and the three others are on the VL domain (L1, L2 and L3).
The vast majority of immunoglobulins are bivalent and monospecific molecules carrying the same specificity on both arms as they are composed of two identical heavy chain polypeptides and two identical light chain polypeptides.
Monoclonal antibodies have emerged as a successful and attractive class of molecules for therapeutic intervention in several areas of human disease. However, targeting or neutralizing a single protein is not always sufficient to achieve efficacy in certain diseases which limits the therapeutic use of monoclonal antibodies. It is increasingly clear that in a number of indications neutralizing one component of a biological system is not sufficient to achieve efficacy. One solution to this problem is the co-administration of several monoclonal antibodies. This approach is however complicated by regulatory aspects if the antibodies to be combined have not been previously approved individually. Moreover, combination approaches are also costly from a manufacturing perspective. Accordingly, there exists a need for antibodies and therapeutics that enable targeting of multiple antigens with a single molecule, as well as a need for efficiently purifying and isolating these multi-specific antibodies. There also exists a need for efficiently purifying and isolating intact antibodies from mixtures that contain antibodies, antibody fragments and/or antibody components.